Schema and instance validation
Use the supplied example or your own schema. Check Schema runs without an instance; Validate checks both documents.
Inputs and references are processed in this browser; no validation data is uploaded and no remote reference is fetched.
Ready for a manual check.
A JSON Schema validator catches a string where your API expects an integer, a missing required key or an unexpected property. Syntactically correct JSON can still violate all three rules. Keep the contract beside the captured response while investigating the mismatch.
Validate JSON against schema constraints without silently repairing the evidence. A null value is different from a missing key, and a default annotation does not make an absent field appear.
The JSON Schema validator reports the instance location beside the schema location. A type error at /users/0/age leads to the rule for that value; a required error can point to its parent and name the missing property in its parameters.
Import dependent schemas instead of copying every definition into the root. Each reference file registers its absolute $id. Relative references resolve against the schema base URI, while the filename remains only a display label.
The selector defaults to 2020-12. Match an explicit $schema declaration before running; a conflicting declaration fails. Draft-07 tuple arrays use items, while 2020-12 uses prefixItems, so a selector change is not a schema migration.
Check Schema parses, checks and compiles the root and every imported dependency without reading the instance. Add reference files with unique absolute $id values without fragments. A missing reference stops compilation instead of weakening the contract.
Validation is manual; Ctrl/Cmd+Enter runs the instance check. Editing either document, changing a setting or importing a dependency cancels the previous task and disables export. Replacing examples, clearing or removing files requires preview and Apply; Undo restores the prior state.
This JSON Schema validator supports draft-07, 2019-09 and 2020-12 through Ajv. Conditional rules and composition are evaluated under the selected dialect. Unknown keywords fail compilation, so an unrecognized constraint cannot quietly turn into a successful check.
JSON Schema validation leaves format disabled initially. Enable it for the built-in ajv-formats checks such as email, date-time, URI and UUID. An unknown format then fails compilation. The switch never changes the independent behavior of pattern.
Malformed JSON, invalid schema keywords, unresolved references and data violations are different failure stages. The online JSON Schema validator keeps those stages distinct. Only a completed schema or instance report can be copied; engine explanations remain in their original English.
The engine stops early where possible, though a composition rule can produce several branch errors. Inspect instancePath, schemaPath, keyword and parameters together. Lists show 50 entries at a time; the JSON download includes the complete accepted report.
An object may have no required properties. Defining properties only describes values when those keys exist. Add required for mandatory keys and type: object when non-object values must also fail; this validator will not add either rule for you.
Check the draft and the shape of items. In draft-07, an array of schemas describes tuple positions rather than a repeated rule. For homogeneous elements use a single items schema; 2020-12 uses prefixItems for tuple positions.
Format is an annotation by default here. Enable format checking to apply the supported date and other built-in checks. It still must be used with the intended value type; a format name is not a substitute for type: string.
The default keyword describes a proposed value; it does not insert data in this tool. Missing required fields still fail, even when a default is present. Populate the value in your application explicitly if that is your contract.
additionalProperties only sees properties and patternProperties evaluated in its own schema context, not arbitrary declarations inside anyOf. Review where you close the object; in newer drafts, unevaluatedProperties may express the intended combined constraint.
Have a schema case we should examine?
Use the JSON Schema validator with both accepted and rejected examples. Keep the selected draft and format setting alongside the exported report when reviewing a contract.